code: def units(self):
      return self._units
  
imports: from typing import Union, Optional, List
  from torch import nn
  import torch
  from ..layers import PositionwiseFFN
  from ..attention_cell import MultiHeadAttentionCell, gen_mem_attn_mask, gen_self_attn_mask
  from ..utils import to_torch_dtype
label_desc: Use image node_id 2 for calling the TransformerDecoder obj's underlying member method code with example usage: obj.units() and returns: self